A new way of checking up on care homes for the elderly in England will put vulnerable residents at greater risk, says a union representing inspectors.
Unison claims the system, which relies more on written self-assessments, will mean thousands of homes will avoid inspections if they look good on paper.
But the Care Quality Commission, which introduced the system, said it would let inspectors focus on failing homes.
It also released figures it said showed adult care had improved significantly.
The new system replaces yearly automatic inspections for all homes.
It came into force in October and now means that homes which provide a good written self-assessment may not be inspected again, unless there is a serious complaint made about them to the commission (CQC).
Unison, which says it represents about 700 inspectors, claims that the workforce numbers have halved since 2004.
Its officer for the CQC, Helga Pile, is concerned about the changes, and said the new inspections would take just a couple of hours, instead of a whole day.
She said: "Our members are really concerned about the lack of ability to really go into homes, spend enough time on site, really talking to people finding out about what is going on."
The carer who blew the whistle on a care home scandal in Somerset in 2007 is also warning the new system would have meant her own care home could have avoided inspections for years on end.
It was because Sarah Barnett raised her concerns over several deaths at Parkfields Care home in Butleigh in Somerset, that its nurse manager was found guilty of killing a 97-year-old resident and stealing drugs to feed her own addiction.
Rachel Baker was sentenced to 10 years in prison earlier this year for the manslaughter of Lucy Cox.
Ms Barnett said: "My personal experience is that people will not blow the whistle, even if they have clear knowledge of what's been happening.
"And as for relying on relatives or people in the community, then you are relying on people who have no medical knowledge and are assuming they will raise concerns."
But the CQC has defended the new arrangements, which it says will allow time to concentrate on homes that are failing.
CQC director for the South West Ian Biggs said: "I can see that a move away from a one-size-fits-all regulatory regime of inspecting every six months, or every year… to a system that is more flexible that acts swiftly when we get information, is a new system.
"And everybody needs to get confident about how that system can work.
"I think we can rely on whistleblowers. We need to encourage them and we need to show them that if they report and whistleblow to us then we will act quickly and responsibly."
But a senior inspector for the CQC in England, who wants to remain anonymous, told the BBC: "Larger private providers could be good at filling out forms that can hide a multitude of sins.
"Therefore there will be no need for us to go out and check. As long as the assessments are done, we look like we have done our job.
"It is only when there are gaps in paperwork that we need to seek more information from a provider. We just don't know what's going on in care homes."
The CQC has published its final assessment of care provision under the old system.
It said 83% of care homes, home care services, nursing agencies and shared lives schemes were rated good or excellent, compared with 69% in 2008.
People were increasingly being supported to live in their own homes, rather in residential facilities, it said, and overall the quality of social care commissioned by councils was improving.
But CQC chief executive Cynthia Bower said "pockets of poor practice" remained.
The regulator also warned that further growth in provision would be needed to meet future needs.